In general, fats and oils such as rapeseed oil, rice oil, soybean oil, and cottonseed oil are in the form of liquid at normal temperature. These liquid fats and oils are stored at low temperatures in a refrigerator, cold climates, or the like, whereby a wax component or a high-melting point triglyceride is crystallized. Consequently, there are some disadvantages that fluidity of the oils is lost and that white turbid or separation is caused, thereby lowering their commercial values.
In addition, at present, palm oil has been remarked in fats and oil industries, and the amount of production thereof is in the second place next to soybean oil in the world ranking for vegetable fats and oils, so that palm oil has become a raw material indispensable in the fats and oils industries. As liquid fats and oils, a composition of fats and oils containing palm oil has been proposed. However, the fats and oils derived from palm oil contain POP(2-oleo-1,3-dipalmitin), which is a triglyceride component having a high melting point, so that there are some disadvantages that crystal growth takes place at low temperatures, thereby generating cloudiness.
In order to overcome these disadvantages, liquid fats and oils is produced by adding a solvent or the like to raw material fats and oils, or produced by fractionation by carrying out a so-called wintering process of directly cooling raw material fats and oils to precipitate out a solid fat which is causation of crystallization, and thereafter separating the precipitates by a means such as dropping, centrifugation, or filtration. For example, liquid fats and oils used in mayonnaise or salad dressings that are stored at low temperatures is produced by a method such as controlling the conditions for a wintering process, thereby removing an even larger amount of solid fats and oils, or subjecting raw material fats and oils previously subjected to transesterification to lower crystallinity to a wintering process, or the like.
However, a method of removing a solid fat by a wintering process is likely to lead to the lowering of productivity or the lowering of a production yield of liquid fats and oils depending upon the processing capacity, thereby making it likely to increase in its production cost.
The palm oil can be fractionated into a high-melting point component palm stearin and a low-melting point component palm olein by a wintering process, and the palm olein can be further separated into a high-melting point component PMF (palm mid fraction) and a low-melting component super olein. However, although the high-melting point triglyceride component is notably reduced in the super olein, the cloud point is still several degrees° C., so that crystals are precipitated in storage in a refrigerator, or cold climates, or in the wintry season, thereby making it difficult to merchandize for liquid fats and oils such as fats and oils for households for which transparency is important.
In view of the above, techniques of inhibiting crystal growth of fats and oils using a specified polyglycerol fatty acid ester have been reported (see Patent Publications 1 to 5). In addition, Patent Publication 6 discloses a polyglycerol fatty acid ester having excellent solubilizability and emulsifiability.